Most airsoft guns are also capable of firing small plastic pellets which are generally used during target practic.
It is the power that separates a standard paintball gun from an airsoft pistol. High-powered gas cylinders drive paintball guns while springs, electronic firing mechanisms or compressed gas are used to release projectiles from an airsoft paintball pistol. Most airsoft guns, because of the way they are powered, are more effective in a smaller arena as they lack the range and accuracy. They just weren't designed with long range shooting in mind.
When it comes to choosing between an airsoft pistol or a paintball pistol, just ask yourself what size field you will most often be playing. If you are playing full-out woodsy paintball, then you definitely need to go with a standard paintball pistol. However, if you are working in a smaller range, target practicing or are more of a collector, then an airsoft pistol is definitely for you.